Free Ringtone Maker
Turn any sound into a ringtone or notification tone for Android and iPhone.
Tip: ringtones work best between 15 and 30 seconds. Drag on the waveform to select.
How to set it as your ringtone
Android: copy the MP3 to your phone, then Settings → Sound → Phone ringtone (or Notification sound) → choose the file.
iPhone: iOS needs an .m4r file added through GarageBand or Finder/iTunes. Open the MP3 in GarageBand on your iPhone, then Share → Ringtone.